I ve checked the typeclasses and I think

Question

< simon vergauwen> I ve checked the typeclasses and I think I can do `PersistentCollection` + `PersistentMap` only with `Semigroup` `Monoid` `Foldable` `Functor` and `FunctorFilter` There is one question though Implementing removal with `FunctorFilter` isn t going to be ineffective I mean it is `O n ` vs `O log n ` or even `O 1 ` in some of the cases Is there a typeclass for explicit removal instead of filtering

addamsson · Answer

There is also an interesting question do we even want to differentiate between `PersistentCollection` and `PersistentMap`

addamsson · Answer

In Clojure for example maps are also collections of paris

addamsson · Answer

it would make sense to just have 1 common ancestor for all persistent collections and go from there

simon.vergauwen · Answer

Yes you can do the same

simon.vergauwen · Answer

This works based on partial type application Do you know how that works

addamsson · Answer

I m not sure

addamsson · Answer

is it similar to partial function application

addamsson · Answer

I m a FP newbie

simon.vergauwen · Answer

It s similar yes A simple example `List lt A gt ` takes 1 type parameter to become a real type i e List + Int = List lt Int gt When we take `Functor` it takes a type that takes 1 type parameter or it takes a Higher kind type of rank 1 gt This is so we can define `fun lt A B gt List lt B gt map f A gt B List lt B gt ` here we require 2 generic types in the function and apply them to the type of Functor `Functor lt ForList gt `

simon.vergauwen · Answer

This happens by doing `Kind lt ForList A gt ` where you can apply a type to `ForList` using the `Kind` interface

simon.vergauwen · Answer

However `Map lt A B gt ` takes 2 parameters so we need to somehow turn it into a type that only takes 1 parameter so we can use it with `Functor` Again you can do this with `Kind` so let s say we d want to use `String` as `A` or key in the map we do `Kind lt ForMap String gt ` This still takes another kind parameter before we can consider the type a `Map`

simon.vergauwen · Answer

Hope that makes some sense sweat smile

simon.vergauwen · Answer

gt Is there a typeclass for explicit removal instead of filtering I had to double check but I am not sure if we currently have something like that It s a pattern available in `Optics` by using `At` <https github com arrow kt arrow blob master modules optics arrow optics src main kotlin arrow optics typeclasses At kt L128>

addamsson · Answer

I checked `At`

addamsson · Answer

it is not good as it only modifies an element

addamsson · Answer

We need a `remove` operation

addamsson · Answer

So how would `ForMap` look like

addamsson · Answer

do I have to do something extra to implement `Monoid lt PersistentCollection lt E gt gt ` `Foldable lt E gt ` `Functor lt E gt ` and `FunctorFilter lt E gt `

addamsson · Answer

apart from doing this

addamsson · Answer

``` interface PersistentCollection lt E gt Monoid lt PersistentCollection lt E gt gt Foldable lt E gt Functor lt E gt FunctorFilter lt E gt ```

addamsson · Answer

I m not sure how to return a `Kind` or an `Eval`

raulraja · Answer

you would not inherit those interfaces but provide bridge extensions for them

raulraja · Answer

what is the type signature of `remove` applied to a concrete type

addamsson · Answer

detailed here right

addamsson · Answer

addamsson · Answer

`fun remove element E PersistentCollection lt E gt `

addamsson · Answer

or rather

addamsson · Answer

`PersistentCollection lt E gt fun remove element E PersistentCollection lt E gt `

addamsson · Answer

so you have a `remove` function for each collection type

addamsson · Answer

`Set` and `List` for now

addamsson · Answer

oh wait a second

addamsson · Answer

is this what `Kind` is used for

addamsson · Answer

`Kind lt ForPeristentCollection E gt `

addamsson · Answer

although it is not very useful to talk about `PersistentCollection`

addamsson · Answer

since all operations should return either a `PersistentSet` or a `PersistentList`

addamsson · Answer

not a collection

addamsson · Answer

that would just replicate the problem the stdlib has

simon.vergauwen · Answer

That s why you need `ForPersistentSet` and `ForPersistentList` then you can apply them to a type parameter using `interface Kind lt F A gt ` This results in `typealias PersistentSetOf lt A gt = Kind lt ForPersistentSet A gt ` and then you should inheret from the typealias ` higherkind interface PersistentSet lt A gt PersistentSetOf lt A gt ` The annotation will generate all the boilerplate for you so you only have to inherit from the typealias and add the annotation

simon.vergauwen · Answer

To go from `PersistentSetOf lt A gt ` to `PersistentSet lt A gt ` you have to call `fix ` because the compiler currently doesn t understand higher kinded types so we have to write some boilerplate This small piece of boilerplate will disappear when we release the compiler plugin for kinds

simon.vergauwen · Answer

You can implement the `Functor` `object PersistentSetFunctor Functor lt ForPersistentSet gt ` When we fill in all the generics for map it looks like this `fun lt A gt PersistentSetOf lt A gt map f A gt B PersistentSet lt A gt `

addamsson · Answer

Given that I get most of the functionality from the aforementioned typeclasses

addamsson · Answer

there is really no point in having a `PersistentCollection` at all

simon.vergauwen · Answer

Similarly you can do the same with `ForPersistentList` and `PersistentMapPartialOf lt String gt `

addamsson · Answer

thanks < simon vergauwen>

addamsson · Answer

i ve just found the relevant docs

simon.vergauwen · Answer

You re very welcome +1

addamsson · Answer

addamsson · Answer

designing data structures without inheritance is kinda new for me smile

simon.vergauwen · Answer

Sounds like a fun time D

addamsson · Answer

it is

addamsson · Answer

i m almost done with HAMT

addamsson · Answer

although there is already a better version CHAMP

addamsson · Answer

there is one problem though

addamsson · Answer

if I m using the Arrow setup I ll have to replicate it in my project

addamsson · Answer

which seems tedious

addamsson · Answer

do you have any suggestions < simon vergauwen>

raulraja · Answer

gt if I m using the Arrow setup I ll have to replicate it in my project Can you elaborate in what you mean by that

addamsson · Answer

The original concept was that I ll implement the VAVR port in my own project

addamsson · Answer

and backport it to Arrow

addamsson · Answer

this is because of the MPP requirement

addamsson · Answer

< simon vergauwen> suggested that I should copy the necessary interfaces from Arrow to my project

addamsson · Answer

but given the kapt magic Arrow does this might not be an option here

addamsson · Answer

btw HAMT is working

addamsson · Answer

I just need to test the hell out of it

raulraja · Answer

Can t you just depend on arrow core and add the arrow meta kapt plugin on your project Then if you wish to contribute it to arrow we can just migrate the repo and rename it to arrow collections or whatever it makes sense

raulraja · Answer

Should be as easy as adding the arrow core dep for 0 9 1 SAPSHOT and the Gradle plugin for arrow meta

raulraja · Answer

addamsson · Answer

No I can t my project is MPP

addamsson · Answer

99 of the code is in common modules

addamsson · Answer

That s why I asked whether the core interfaces are MPP in Arrow

addamsson · Answer

then it turned out that this is not how you use Arrow in the first place so I think we re at an impasse right now

addamsson · Answer

How can I help with the MPP effort btw